The present invention relates to the improvement of materials through low temperature treatment. More particularly, the invention relates to the improvement of abrasive wear, corrosive wear, erosive wear and related physical characteristics, i.e., stress relief and stabilization, in a wide variety of materials, including metals, metallic alloys, carbides, plastics and ceramics, through deep cryogenic processing.
Ultralow temperature treatment (-300.degree. F. to -320.degree. F.) or deep cryogenic processing of metals, particularly metals in the form of cutting tools, has been known to show some improvement in abrasion and corrosion resistance along with reduction of internal stresses and improved material stability. Thus, ultralow temperature treatment of metal tools results in improvement in the wear resistance of such tools (increases tool life) whereas the heat treatment of metal tools is utilized to obtain desired combinations of metal hardness, toughness and ductility. With deep cryogenic processing there is no change in the dimension, size or volume of the parts or items treated, and the hardness of the items is not altered.
Deep cryogenic processing has been used for the wear improvement treatment of: industrial cutting tools (dies, stamping dies, drills, end mills, taps, reamers, hobs, gear cutters, broaches, etc.); hand tools (knives, chisels, plane irons, saws, punches, files, etc.); turbine blades; rotating and sliding machine items (ball and roller bearings, piston rings, bushings, etc.); springs; resistance welding electrodes; and castings and forgings. The materials treated have included: steel and steel alloys; titanium and titanium alloys; high-nickel alloys; copper and brass; aluminum and aluminum alloys; metal carbides and nitrides; ceramic materials; and a wide variety of plastic materials including nylons and teflons.
Ultralow temperature treatment has been principally carried out using liquid nitrogen as the cooling medium. Temperature descent from ambient temperature to deep cryogenic temperatures of -300.degree. F. to -320.degree. F. takes, under most known cryogenic procedures, about 8 hours. The parts or items under treatment are maintained at the ultralow temperature for 10-20 hours and then returned to ambient temperature over a period of as much as 30 hours. The treatment results are frequently unpredictable.
For industrial items made of steel and steel alloys, deep cryogenic treatment seems to remove the kinetic energy of the atoms making up such items. There is a normal attraction between atoms but their energy of motion tries to keep them apart unless such energy is removed, as by low temperature treatment. Treatment at below -300.degree. F. transforms retained soft austenite (one form of crystalline steel) into the more stable hard martensite form of steel. During this transformation, additional smaller carbon carbide particles are released and evenly distributed throughout the mass of the material. These smaller carbide particles help support the martensite matrix. In cutting tools, this reduces the heat buildup on the cutting edge and this in turn increases the wear resistance of the tools. Improvements in the resistance to wear can and does reduce the cost of products produced by machine tools because of longer tool life, less scrap, fewer rejections and less production downtime. It has been reported that deep cryogenic treatment of tool steel alloys has resulted in improvement in wear resistance by factors of as much as 2-6 times.
It is an object of the present invention to provide an improved treatment chamber for carrying out the deep cryogenic processing of metallic, carbide, ceramic and plastic parts and items to increase their wear resistivity with a high degree of predictability.
It is a further object of the invention to provide unique apparatus for effecting the deep cryogenic treatment of metallic, carbide, ceramic and plastic parts and items under optimum time-temperature profiles to achieve highly efficient processing results and predictable repeatability.
It is another object of the invention to provide an improved method for carrying out ultralow temperature treatment of metallic, carbide, ceramic and plastic parts and items to increase the wear resistivity of such parts and items.
It is yet another object of the invention to provide an improved method for carrying out the efficient and reliable deep cryogenic treatment of metallic, carbide, ceramic and plastic parts and items utilizing optimum time-temperature processing profiles to increase the wear resistivity and stability of such parts and items.
Other objects and advantages of the invention will be apparent from the following detailed description of the invention, taken with the accompanying drawings.